Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!swrinde!elroy.jpl.nasa.gov!lll-winken!sun-barr!olivea!tymix!tardis!jms From: jms@tardis.Tymnet.COM (Joe Smith) Newsgroups: comp.sys.amiga.audio Subject: Re: Disable low-pass filter on Amiga 500? Summary: Sometimes good, sometimes bad. Message-ID: <1707@tardis.Tymnet.COM> Date: 10 Apr 91 08:06:56 GMT References: <1391@ssp18.idca.tds.philips.nl> <9103192231.39@rmkhome.UUCP> Reply-To: jms@tardis.Tymnet.COM (Joe Smith) Organization: BT Tymnet, San Jose, CA Lines: 37 I posted this article just after the newsgroup arrived at my site. Since the group was so new, it might not have been picked up by very many sites, so I'm posting it again. Article 1 of comp.sys.amiga.audio: Path: tardis!jms From: jms@tardis.Tymnet.COM (Joe Smith) Newsgroups: comp.sys.amiga.audio Subject: Cases where the low-pass filter is a Good Thing. Message-ID: <1418@tardis.Tymnet.COM> Date: 13 Jan 91 07:46:13 GMT Reply-To: jms@tardis.Tymnet.COM (Joe Smith) Organization: BT Tymnet, San Jose, CA Lines: 22 I was wandering around a the MacWorld Expo today, checking out the new products. One thing that struck me was that most of the digitized audio output did not have a low-pass filter, and it sounded awful. Imagine an audio distorter that, whenever it detects a 2000 Hz tone, it adds a 6000 Hz tone. And when it detects a 1000 Hz tone, it adds a 7000 Hz tone. (When the main sound has a descending pitch, the distortion has a rising pitch.) When human speech is passed through such a distorter, it produces an awful high pitched rattle. The above description is exactly what happens when an audio sample is digitized at 8000 Hz, and played back on a system that does not have a low-pass filter to get rid of the aliasing due to heterodyning. My point is: Be thankful that the Amiga has a low-pass filter on the audio outputs as standard equipment. At medium and low sampling rates, its presence causes a noticable improvement in audio quality. -- Joe Smith (408)922-6220 | SMTP: jms@tardis.tymnet.com or jms@gemini.tymnet.com BT Tymnet Tech Services | UUCP: ...!{ames,pyramid}!oliveb!tymix!tardis!jms PO Box 49019, MS-C51 | BIX: smithjoe | CA license plate: "POPJ P," (PDP-10) San Jose, CA 95161-9019 | humorous dislaimer: "My Amiga 3000 speaks for me."